The invention relates to gas turbine engines, and more specifically to a seal system for providing a fluid leakage restriction between components within such engines.
Gas turbine engines operate by burning a combustible fuel-air mixture in a combustor and converting the energy of combustion into a propulsive force. Combustion gases are directed axially rearward from the combustor through an annular duct, interacting with a plurality of turbine blade stages disposed within the duct. The blades transfer the combustion gas energy to one or more disks, rotationally disposed about a central, longitudinal axis of the engine. In a typical turbine section, there are multiple, alternating stages of stationary vanes and rotating blades disposed in the annular duct.
Because the combustion gas temperature may reach 2000° F. or more, some blade and vane stages are cooled with lower temperature cooling air for improved durability. Air for cooling the first-stage blades bypasses the combustor and is directed to an inner diameter cavity located between a first-stage vane frame and a first-stage rotor assembly. The rotational force of the rotor assembly pumps the cooling air radially outward and into a series of conduits within each blade, thus providing the required cooling.
Because the outboard radius of the inner cavity is adjacent to the annular duct carrying the combustion gases, it must be sealed to prevent leakage of the pressurized cooling air. This area of the inner cavity is particularly challenging to seal, due to the differences in thermal and centrifugal growth between the stationary first-stage vane frame and the rotating first stage rotor assembly. In the past, designers have attempted to seal the outboard radius of inner cavities with varying degrees of success.
An example of such a seal is disclosed in U.S. Pat. No. 4,701,105, issued to Cantor and Farrand and entitled “Anti-Rotation Feature for a Turbine Rotor Faceplate”. In this example, a multi-step labyrinth seal separates the inner cavity into two regions of approximately equal size, an inner region and an outer region. Cooling air in the inner region is pumped between the rotating disk and labyrinth seal into the hollow conduits of the blades while the outer region is fluidly coupled to the annular duct carrying the combustion gases. A labyrinth seal's lands are typically pre-grooved to prevent interference between the knife-edge teeth and the lands during a maximum radial excursion of the rotor. By designing the labyrinth seal for the maximum radial excursion of the rotor assembly, the leakage restriction capability is reduced during low to intermediate radial excursions of the rotor assembly. Any cooling air that leaks by the labyrinth seal is pumped through the outer region and into the annular duct by the rotating disk. This pumping action increases the temperature of the disk in the area of the blades and creates parasitic drag, which reduces overall turbine efficiency. The rotating knife-edges also add additional rotational mass to the gas turbine engine, which further reduces engine efficiency.
Another example of such a seal is disclosed in U.S. Pat. No. 5,310,319, issued to Grant and Hoyt and entitled “Free Standing Turbine Disk Sideplate Assembly” and U.S. Pat. No. 5,522,698, issued to Butler and Gernhardt and entitled “Brush Seal Support and Vane Assembly Windage Cover”. As this example illustrates, a brush seal separates the inner cavity into two regions, an inner region and a smaller, outer region. A freestanding sideplate assembly defines a disk cavity, which is in fluid communication with the inner region. Cooling air in the inner region enters the disk cavity and is pumped between the rotating sideplate and disk to the hollow conduits of the blades. The seal's bristle-to-land contact pressure increases during the maximum radial excursions of the rotor and may cause the bristles to deflect and set over time, reducing the leakage restriction capability during low to intermediate rotor excursions. Any cooling air that leaks by the brush seal is pumped into the outer region by the rotating disk. This pumping action increases the temperature of the disk in the area of the blades and creates parasitic drag, which reduces overall turbine efficiency. The freestanding sideplate and minidisk also adds rotational mass to the gas turbine engine, which further reduces engine efficiency.
Copending U.S. patent application Ser. No. 11/146,801 entitled “Hammerhead Seal” (applicant reference number EH-11279), Ser. No. 11/146,798 entitled “Combined Blade Attachment and Disk Lug Fluid Seal” (applicant reference number EH-11598), and Ser. No. 11/146,660 entitled “Blade Neck Fluid Seal” (applicant reference number EH-11507), all filed Jun. 7, 2005, disclose improved sealing systems. The disclosures of these applications are incorporated by reference herein as if set forth at length.